The invention relates to materials, especially optical materials, formed on a substrate surface in which stress within the material is reduced or eliminated by the placement or inclusion of a decoupling layer between the material and the substrate surface. The invention further relates to optical devices and integrated optical circuits incorporating optical materials located on a decoupling layer. In addition, the invention relates to methods for the production of optical materials on a stress relieving layer, the production of the stress relieving layer and integrated optical devices incorporating the stress relieved optical materials.
The consolidation or integration of mechanical, electrical and optical components into integral devices has created enormous demands on material processing. Furthermore, the individual components integrated in the devices are shrinking in size due to new materials and new technologies. Therefore, there is considerable interest in the formation of specific compositions applied to substrates. In order to form optical devices with high quality optical coatings from these materials, the coatings must be highly uniform. Interest in forming highly uniform materials for these coatings has sparked the development of processes for producing optical coatings.
Presently used optical communication light wavelengths are from less than about 0.6 microns to more than about 1.6 microns. Optical waveguides generally have dimensions larger than the wavelength used. Thus, optical structures can have dimensions from less than a few microns to more than about 100 microns depending on optical mode requirements, design, function and other factors.
An explosion of communication and information technologies including internet-based systems has motivated a worldwide effort to implement fiber optical communication networks to take advantage of a very large potential bandwidth. The capacity of optical fiber technology can be expanded further with implementation of Dense Wavelength Division Multiplexing (DWDM) technology. With increasing demands more channels are needed to fulfill the system functions. Integrated components can be used to replace discrete optical components to supply the desired capacity.
Optical components can be integrated onto a planar chip-type base analogous to an electronic integrated circuit. By placing the optical components onto an integrated chip with a substrate, such as a silicon wafer, many optical components can be highly integrated into a compact structure with a small footprint. For the mass production of these integrated optical chips, existing semiconductor technology, such as lithography and dry etching, can be involved advantageously in appropriate steps of the production process.
The production of integrated optical components requires the deposition of high quality optical materials onto the substrate surface. Furthermore, the optical materials must be fashioned into specific devices. In particular, a significant technology for the integration of optical components centers around the production of planar waveguides. Semiconductor or similar approaches have been used to form the waveguides following the deposition of optical materials.
Basic characteristics of optical film coatings include surface quality, film uniformity and optical quality. Optical quality refers to many properties including absorption, scattering, loss and transmission. Optical quality also includes the uniformity of optical properties, such as index of refraction, and low bi-refringence. In addition, optical quality includes interface quality, such as the interface between the core layers and cladding layers. Current benchmarks are established, for example, by glass fibers, planar waveguide glass, lithium niobate, and InP. For silica (SiO2) glass forms generally have the highest optical quality, while for other materials single crystal forms have the highest quality optical transmission.
Several approaches have been used and/or suggested for the deposition of the optical materials. These approaches include, for example, flame hydrolysis deposition (FHD), chemical vapor deposition (CVD), physical vapor deposition (PVD), sol-gel chemical deposition and ion implantation. FHD and CVD are two common methods for commercial implementation of planar waveguides. Flame hydrolysis and forms of chemical vapor deposition have also been successful in the production of glass fibers for use as fiber optic elements. Flame hydrolysis deposition involves the use of a hydrogen-oxygen flame to react gaseous precursors to form particles of the optical material as a coating on the surface of the substrate. Subsequent heat treatment of the coating can result in the formation of a uniform optical material, which generally is a glass material. The next generations of integrated optical components will have stricter tolerances for uniformity and purity.
Approaches have been developed for the production of highly uniform submicron and nanoscale particles by laser pyrolysis. Highly uniform particles are desirable for the fabrication of a variety of devices including, for example, batteries, polishing compositions, catalysts, and phosphors for optical displays. Laser pyrolysis involves an intense light beam that drives a chemical reaction of a reactant stream to form highly uniform particles following the rapid quench of the stream after leaving the laser beam. Laser pyrolysis approaches have been adapted for the production of highly uniform optical materials on substrate surface using an approach called light reactive deposition.
In a first aspect, the invention pertains to a structure comprising a substrate having a surface, a release layer on the surface of the substrate and a first uniform material on top of the release layer. The release layer includes powders or partly sintered powders. The invention further includes a method for transferring a layer of optical material to a receiving substrate surface. The method involves applying separation forces to transfer to the receiving substrate a uniform material from a transfer material in contact with the receiving substrate surface. The transfer material includes a substrate having a surface, a release layer on the surface of the substrate and a first uniform material on top of the release layer. The layer of transferred material includes the first uniform material of the transfer material.
In another aspect, the invention pertains to a structure comprising a substrate having a surface and an optical material having a thickness from about 3 microns to about 50 microns, which is located on a substrate surface. In this structure, the optical material is free of stress.
In a further aspect, the invention pertains to a method for forming a structure with a uniform material on a substrate with a release layer between the uniform material and the substrate. The method includes depositing a layer of powder on a substrate and heating the powder layers. The powder in the layer has a lower sintering temperature at the top than the powder in the layer adjacent the substrate. The heating of the powder layers converts the top of the powder layer to a uniform material while the powder layer adjacent the substrate becomes a release layer.
In an additional aspect, the invention pertains to another method for forming a uniform material on a substrate surface with a release layer between the uniform material and the substrate. This method includes heating a powder coating on the surface of the substrate from above to produce the uniform material the surface and a release layer between the substrate surface and the uniform optical material.
Furthermore, the invention pertains to a substrate-less planar optical structure comprising a plurality of optical glass layers with different indices-of-refraction from each other. A thickness through the entire structure is no more than about 1 mm. Also, a planar projection of the structure with a maximum surface area has a minimum edge-to-edge distance of a segment passing through the center of the projected area of at least about 1 cm.